Send GPS data with every measurement?

[proffalken]

Hi,

I've noticed that because the GPS data is only sent on channel 4, correlating events (PAX/BME680 measurements etc) against GPS position is nigh-on impossible in InfluxDB backends unless you somehow store the value from channel 4 somewhere when it arrives, and then add it in via a custom script each time a packet from that device arrives with other sensor data in it.

Is it possible to configure the device so that it sends the GPS data as well as the sensor data?

For example, it would be great if I could get a payload that includes both the lat/long/altitude and the VOC level from the BME680 in the same packet so I can graph the VOC level against the GPS co-ordinates

[cyberman54]

Spreading sensor values on different ports was done intentionally, to keep the payload as small as possible for different use cases.

If you need a combined payload it's very simple to modify the code. Just add methods of class payload (found in payload.h) as you need in senddata.cpp.

For example, to combine pax, VOC and GPS:

case COUNT_DATA:
      payload.reset();
      payload.addCount(macs_wifi, MAC_SNIFF_WIFI);
      payload.addBME(bme_status);
      payload.addGPS(gps_status);
      SendPayload(COUNTERPORT, prio_normal);

Be aware that you may see large delays when transmitting huge payloads on a LoRaWAN network, depending on duty cycle and spreading value of transmission.

The priority parameter of class SendPayload has no impact on network transmission, it affects the waiting queue on the device only. With huge payloads you will probably get queues. That means on server side the receiving timestamp and gps location data may not match. To avoid this you can send gps data with prio_high, thus location data will be transmitted last in - first out. For this reason it makes sense to have a separate GPS channel, like Cayenne does.

[proffalken]

Magic, thank you!

I don't necessarily need all the metrics in the same payload, but having GPS to accompany the various other metrics is awesome.

[cyberman54]

Remember: if you combine payload you will get delays when transmitting via LoRaWAN, so your GPS locations won't match the timestamps. This is a problem e.g. when used paxcounter device with ttnmapper (but, in general, this works)